Method and system for establishing a correct lead when firing at a moving target

ABSTRACT

The invention relates to a method and device for computing and providing a correct lead angle between the direction of fire and the line of sight when firing a projectile at a moving target with a weapon and sight system in which the weapon and the sighting instrument are mechanically and/or electrically coupled to each other so as normally to move uniformly. The correct lead angle is computed during a predetermined limited time interval the length of which is proportional to the range to the target. During this computation interval the line of sight of the sighting instrument is maintained pointed directly at the moving target and the weapon is moved uniformly with the sighting instrument without any relative angular velocity between the line of sight of the sighting instrument and the direction of fire of the weapon, while simultaneously the angular velocity of the line of sight is integrated. At the end of the computation interval, over which the angular velocity of the line of sight is integrated, the direction of fire of the weapon and the line of sight of the sighting instrument are deflected from each other by an angle proportional to the result of the integration and in such a direction that the direction of fire of the weapon will lead the line of sight of the sighting instrument as seen in the direction of the target tracking.

United States Patent Erhard 51 Aug. 22, 1972 [54] METHOD AND SYSTEM FORESTABLISHING A CORRECT LEAD WHEN FIRING AT A MOVING TARGET [72]Inventor: Rune Torsten lsidor Erhard, Karlskoga, Sweden [73] Assignee:Aktiebolaget Bofors, Bofors, Sweden [22] Filed: Dec. 22, 1969 [21] Appl.N0.: 886,981

[30] Foreign Application Priority Data Jan. 3, 1969 Sweden ..96/69 [52]US. Cl. ..33/238, 89/41 AA [51] Int. Cl ..F4lg 3/08 [58] Field of Search..33/49 R, 49 A, 49 B, 49 C; 89/37 A, 41 AA, 41 B, 41E

[56] References Cited UNITED STATES PATENTS 3,277,282 10/ I966Kuhlenkamp ..33/49 C X 2,660,794 12/1953 Goertz et al. ..33/49 C2,538,821 1/1951 Wheeler ..33/49 B 2,968,871 1/1961 Hammond, Jr ..33/49B 3,135,053 6/1964 Newman et al. ..33/49 C Primary Examiner-William D.Martin, Jr. Attorney-Harte & Baxley [57] ABSTRACT The invention relatesto a method and device for computing and providing a correct lead anglebetween. the direction of fire and the line of sight when firing aprojectile at a moving target with a weapon and sight system in whichthe weapon and the sighting instrument are mechanically and/orelectrically coupled to each other so as normally to move uniformly. Thecorrect lead angle is computed during a predetermined limited timeinterval the length of which is proportional to the range to the target.During this computation interval the line of sight of the sightinginstrument is maintained pointed directly at the moving target and theweapon is moved uniformly with the sighting instrument without anyrelative angular velocity between the line of sight of the sightinginstrument and the direction of fire of the weapon, while simultaneouslythe angular velocity of the line of sight is integrated. At the end ofthe computation interval, over which the angular velocity of the line ofsight is integrated, the direction of fire of the weapon and the line ofsight of the sighting instrument are deflected from each other by anangle proportional to the result of the integration and in such adirection that the direction of fire of the weapon will lead the line ofsight of the sighting instrument as seen in the direction of the targettracking.

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RUNE TORST'EN lS/DOR ERHARD A'rraklvtrs METHOD AND SYSTEM FORESTABLISHING A CORRECT LEAD WHEN FIRING AT A MOVING TARGET The presentinvention relates to a method and a device for providing a correct leadwhen firing projectiles at a moving target with a weapon and sightsystem including a weapon and a sight which are mechanically and/orelectrically coupled to each other so that the direction of fire of theweapon and the line of sight of the sighting instrument normally moveuniformly during the target tracking process. In particular theinvention is related to vehicle carried weapons, as for instance weaponsin tanks, where the weapon may be mounted on the vehicle so as to bemovable in azimuth as well as elevation relative to the vehicle oralternatively be fixed in the vehicle, in which latter case the weaponis aimed by movement of the entire vehicle. However, the invention canalso be used at stationary weapons. In particular the invention isrelated to such weapon and sight systems in which the sight is mountedon the movable portion of the weapon so that it participates in or atleast is affected by the aiming of the weapon, but the invention canalso be used in weapon and sight systems in which the weapon and sightare separate and can be individually aimed so that the aiming of theweapon does not directly affect the sight.

When firing at a moving target with a weapon and sight system of thetype mentioned above the sight operator or gunner keeps the line ofsight of the sighting instrument permanently pointed at the movingtarget and at the same time controls the weapon so that the direction offire of the weapon moves uniformly with the line of sight. in a systemwhere the sight is mounted directly on the aimable weapon the line ofsight is generally pointed at the target by aiming of the weapon assuch. As well known, however, at the moment when a projectile is to befired a certain angular deflection must exist between the direction offire of the weapon and the line of sight of the sighting instrumentwhich is pointing at the target. The total necessary deflection angleconsists primarily of two components, namely one component, the socalled lead, which is required due to the movement of the target, and asecond component, the so called superelevation, which is required due tothe curved trajectory of the projectile. The total deflection angleincludes generally also corrections or compensations for instance forthe effects upon the fired projectile from wind forces, for the rotationof the projectile, etc. The present invention concerns primarily thecomputation of the lead angle necessary due to the movement of thetarget but touches also the computation of the other components of thetotal deflection angle between the direction of fire of the weapon andthe line of sight at the moment of firing a projectile.

The lead angle necessary due to the movement of the target is dependenton the angular velocity of the target relative to the site of theweapon, this angular velocity being equal to the angular velocity of theline of sight if the sighting instrument is mounted on or located closeto the weapon and the line of sight is maintained permanently pointed atthe target, the range to the target and the mean velocity of theprojectile fired at the target. For computing the necessary lead angleit is known in the art to measure the angular velocity of the line ofsight continuously during the target tracking and on the basis of thisangular velocity, after low-pass filtering thereof, and a continuouslymeasured value for the range to the target to let a computercontinuously compute the lead angle required due to the movement of thetarget; the deflection angle between the line of sight and the directionof fire of the weapon being continuously adjusted into agreement withsaid computed value. However, a device operating according to thisprinciple becomes comparatively complicated. Further the sight operatormust maintain the line of sight continuously pointed at the target, asany error in the target tracking will give cause to an error in thecomputation of the lead angle and this error will remain for a timewhich is dependent on the time constant for the low-pass filtering ofthe measured angular velocity of the line of sight. Consequently it isnot possible for the sight operator to judge when a sufficient accuracyin the computation of the lead angle has been achieved after an error inthe target tracking. Further, every change in the velocity or thedirection of movement of the target will give cause to a disturbance inthe computation of the lead angle and this disturbance will not beeliminated until after a time unknown to the sight operator.

A system is also known in the prior art, in which the lead anglenecessary due to the movement of the target is provided in that during apredetermined limited time interval, at the beginning of which thedirection of fire of the weapon as well as the line of sight of thesighting instrument are pointing directly at the target and have thesame angular velocity, the line of sight is given an angular velocitywhich is only a predetermined fraction of the angular velocity of theweapon so that during this time interval a continuously increasingdeflection angle is created between the direction of fire of the weaponand the line of sight. At the end of the time interval, when the line ofsight and the direction of fire are once more given the same angularvelocity, the accumulated deflection angle is equal to the lead anglerequired due to the movement of the target. This method has theadvantage that it requires only a comparatively simple computing deviceand that the sight operator must keep the line of sight exactly pointedat the target only at the beginning and that the end of thepredetermined limited time interval in order to produce a correct leadangle. However, at the beginning of such time interval the line of sightis suddenly given a smaller angular velocity than before, wherefore itcannot be avoided that the sight operator loses the target with the lineof sight. Consequently the sight operator must during the limited timeinterval return the line of sight onto the target so that it isaccurately pointed at the target at the end of the time interval. It hasbeen found that this is a very difficult task for the sight operator, asthe predetermined limited time interval must be comparatively short, ofthe order of 1 to 2 seconds. The reason for this is partly than onewishes to fire a projectile at the target as soon as possible and partlythat the target must move with constant velocity and in an unchangeddirection during the time interval if the computation of the lead angleis to be correct. Further, in a system of this type it is comparativelydifficult to .introduce the other necessary components of the totaldeflection angle between the direction of fire and the line of sight,

such as the superelevation and the compensations for wind forces, theprojectile rotation, etc.

An object of the present invention is therefore to provide a method anda device for providing a correct lead when firing at a moving targetwith a weapon and sight system of the type mentioned in the foregoing,

which method puts substantially smaller demands on the skill and thereaction speed of the sight operator and which requires only a simpledevice with a comparatively small number of components for thecomputation of the lead angle necessary due to the movement of thetarget and which device may also be modified by addition of acomparatively small number of additional components to compute also thedeflection angle components necessary for the super-elevation, windcompensation, compensation for the projectile rotation, etc.

Also in the method according to the invention the lead angle necessarydue to the movement of the target is computed during a predeterminedlimited time interval and the method is characterized in that the lineof sight is maintained pointed directly at the target and the directionof fire of the weapon is moved uniformly with the direction of the lineof sight without any relative velocity between the direction of fire andthe line of sight while the angular velocity of the line of sight isintegrated over a predetermined time interval, and that after theintegration interval the line of sight and the direction of fire aredisplaced relative each other by an angle proportional to the result ofthe integration and in a direction such that the direction of fire willlead the line of sight as seen in the direction of the movement of theline of sight.

As according to the method of the invention the lead angle required dueto the movement of the target is computed during a predetermined limitedtime interval, the sight operator has only to ascertain that the line ofsight is accurately pointing at the target at the beginning and at theend of such time interval in order to achieve a correct computation. Asa matter of fact the computation will be correct if the direction of theline of sight relative to the target is the same both at the beginningand at the end of the measuring interval. Thus the computation error isproportional to the difference between the tracking errors at said twoinstants. As the sight operator himself determines the instant when thecomputation interval is started and easily can be informed about the endof the computation interval, the sight operator can easily judge whetherthe computation carried out during the limited computation interval hasbeen sufficiently accurate. Should this not be the case he canimmediately start a new computation interval. As according to the methodof the invention the line of sight is pointing directly at the targetand has an angular velocity equal to the angular velocity of the targetat the beginning of the measuring interval and at this instant no suddencompulsory change outside the control of the sight operator is imposedupon the angular velocity of the line of sight, it is very easy for thesight operator to track the target during the computation interval andto ascertain that at the end of the computation interval the line ofsight is accurately aimed at the target. Thus in contrast to the priorart system for computation of the lead angle during a predeterminedlimited time interval which has been described in the foregoing, nodisturbance whatsoever is imposed upon the target tracking at thebeginning of the computation interval, which disturbance it would benecessary for the sight operator to eliminate before the end of thecomputation interval. Therefore, the computation interval can be shortwithout insurmountable demands being put upon the skill of the sightoperator. It is advantageous to have a short computation interval partlybecause this permits an early firing of a projectile against the targetand partly as the target must move with a constant velocity and in anunchanged direction from the beginning of the computation interval tothe instant of impact of the fired projectile if the computed lead angleis to be valid. The length of the integration interval may be constant,in which case at the end of the integration interval the line of sightand the direction of fire are displaced relative each other by an angleequal to the product of the result of the integration and a computedvalue for the time of flight of the fired projectile.

Alternatively the integration interval may have a length proportional tothe computed time of flight of the projectile, in which case thedirection of fire and the line of sight are displaced relative eachother by an angle directly corresponding to the result of theintegration.

However, the length of the integration interval is preferably made equalto a constant times the range to the target, in which case at the end ofthe integration interval the line of sight and the direction of fire aredisplaced relative each other by an angle proportional to the result ofthe integration divided by a computed value for the mean velocity of theprojectile fired against the target. In this case the device for thecomputation of the necessary deflection angle between the direction offire and the line of sight can be given an especially simple andcomponent-saving design, in particular if the device is adapted tocompute not only the lead angle necessary due to the movement of thetarget but also other components of the total deflection angle, such asthe superelevation, wind compensation, compensation for the projectilerotation, etc.

Since, generally, the weapon and sight can be directed in azimuth aswell as in elevation and also the target is moving in azimuth as well aselevation, the computation of the total lead angle is in conventionalmanner divided into a computation of the lead angle in azimuth andanother computation of the lead angle in elevation, these twocomputations being of course carried out simultaneously. Correspondinglythe device for performing this computation and for displacing the lineof sight and the direction of fire of the weapon relative each other inagreement with the computed lead angle consists in principle of twoportions, one for the azimuth components and the other for the elevationcomponents of the movements of the weapon and the sighting instrumentrespectively.

In the following the invention will be further described with referenceto the accompanying drawing, which illustrates by way of example aweapon and sight system in which the invention is incorporated. in thedrawing:

FIG. 1 is a schematical perspective view of a weapon and sight systemprovided with a device according to the invention, in which system thesight is mounted on the weapon so as to participate in the aimingthereof;

FIG. 2 is a block diagram of the device according to the inventionincorporated in the weapon and sight system in FIG. 1 for computing therequired lead angle and of the devices necessary for the aiming of theweapon and for the introduction of the computed lead angle between thedirection of fire of the weapon and the line of sight; and

FIG. 3 is a diagram illustrating the angular positions of the target,the line of sight and the direction of fire as functions of time duringthe target tracking.

Before the device illustrated in the drawing is described in detail, ashort discussion of the mathematical expressions on which thecomputation of the various components of the total deflection angle isbased will be given. In this discussion following symbols are used:

D range to the target w the angular velocity of the target relative tothe site of the weapon and thesight w the angular velocity of the lineof sight v the muzzle velocity of the projectile v,,,=the mean velocityof the projectile during the time of flight t, the time of flight of theprojectile the lead angle necessary due to the movement of the target4),, superelevation necessary due to the curved trajectory of theprojectile Provided that the line of sight is maintained pointed at thetarget, one has obviously w,, w For the time of flight of the projectileone has tg= l nl (2) As well known the mean velocity of the projectilecan be expressed by the series f m r=( m (4) As well known the necessarysuperelevation 4),, can be approximated by the series where k k and kare constants and in which series generally one or two terms give asufficient accuracy.

For the computation of other components of the total deflection anglethat may be necessary, as for instance compensations for the wind andthe projectile rotation, expressions may be used similar to theexpression (5) given above for the superelevation 1 as well known in theart.

It shall be pointed out here that all the components of the totalnecessary deflection angle between the direction of fire and thedirection to the target that are to be computed are inverselyproportional to the mean velocity v of the projectile, a fact that ismade use of for simplifying the design of the device according to theinvention.

FIG. 1 shows as an example only and very schematically a weapon andsight system including a gun with a barrel 1 which in conventionalmanner is mounted for elevation on a gun mount 2 upon a rotatableplatform 3. Thus the barrel 1 can be directed in elevation as well as inazimuth relative to a supporting member not illustrated in the drawing,which may for instance consist of a vehicle, such as a tank, in whichcase the platform 3 is replaced with the gun turret of the tank. In theillustrated embodiment of the invention the barrel 1 is directed inazimuth, by means of a servomotor M1 and in elevation by means of aservomotor M2. A

tachogenerator T1 is coupled to the servomotor M1 for generating anelectric signal proportional to the angular velocity in azimuth of thebarrel 1 and thus of the direction of fire. In similar manner atachogenerator T2 is coupled to the servomotor M2 for generating anelectric signal proportional to the angular velocity in elevation of thebarrel 1 and thus of the direction of fire.

As shown in FIG. 2, the azimuth motor M1 for the barrel 1 is suppliedwith a control signal through a servo-amplifier F1 and a comparator Clfrom a signal generator S1, such as a potentiometer, which is coupled toa manually, by the gunner, operated control lever 5 which is universallypivoted in a pivot and gearing mechanism 4. The signal generator S1 iscoupled to the lever 5 in such a way that it generates a signalproportional to the deviation angle of the lever 5 from a neutralposition in a predetermined first direction. The output signal from thetachogenerator T1 is fed back in opposition to the comparator C 1.Consequently the servomotor M1 is rate coupled, wherefore the gunner bymeans of the control lever 5 can impart an angular velocity to thebarrel 1 proportional to the deviation of the control lever 5 from itsneutral position in the first direction.

In a similar manner the elevation servomotor M2 for the barrel 1 issupplied with a control signal through a servoamplifier F2 and acomparator C2 from a signal generator S2 which is coupled to the controllever 5 so as to generate an electric signal proportional to thedeviation angle of the lever 5 from its neutral position in a seconddirection which is perpendicular to the first direction. The outputsignal of the tachogenerator T2 is fed back in opposition to thecomparator C2, whereby the servomotor M2 imparts an angular velocity inelevation to the barrel 1 proportional to the deviation angle of thecontrol lever 5 from its neutral position in said second direction.

The weapon and sight system shown in FIG. 1 includes also a sightinginstrument 6 mounted on a portion of the gun which can be directed inazimuth as well as in elevation. In the drawing the sighting instrumentillustrated only very schematically as the specific type or design ofthe sight is of no fundamental importance for the invention. Thus forinstance the sight may be a suitable conventional optical sight, a radarsight or a laser sight. It is only important that the gunner cancontinuously determine the position of the line of sight through thesighting instrument relative to the direction to a target viewed throughthe sight. In the illustrated embodiment it has been assumed for thesake of simplicity that the sight 6 has a line of sight which is fixedrelative to the sight casing and that the sight casing together with theline of sight can be rotated in azimuth relative to the direction of thebarrel 1, that is the direction of fire of the weapon, by means of aservomotor M3 and in elevation by means of a servomotor M4. However, thesighting instrument may of course also be of a type having a line ofsight which is movable in azimuth and elevation relative to the sightcasing, for instance by means of movable optical members, such asmirrors, prisms or hairline crosses. In this case the sight casing ismounted stationary on the layable portion of the gun and the servomotorsM3 and M4 are coupled to those members in the sighting instrument itselfby means of which the line of sight can be moved in azimuth andelevation respectively relative the sight casing. The two servomotors M3and M4 have predetermined starting positions in which the line of sightfor the sighting instrument 6 is parallel to the direction of thebarrel 1. As long as the servomotors M3 and M4 are not rotated fromthese starting positions during a target tracking process the line ofsight remains consequently stationary relative to the direction of fireof the gun and parallel thereto. By viewing a moving target through thesighting instrument 6 and controlling the azimuth motor M1 and theelevation motor M2 respectively for the barrel 1 a gunner canconsequently continuously maintain the line of sight as well as thebarrel aimed directly at the moving target. During this process thesignal produced by the tachogenerator Tl will be proportional to theazimuth angular velocity of the line of sight and thus also of themoving target, whereas the signal produced by the tachogenerator T2 willbe proportional to the elevation angular velocity of the line of sightand thus of the moving target.

An electric signal generator Pl, such as a potentiometer, is coupled tothe servomotor M3 for generating a signal proportional to the rotationangle of the servomotor M3 from its starting position. In similar mannera signal generator P2, for instance a potentiometer, is coupled to theservomotor M4 so as to generate a signal proportional to the rotationangle of the servomotor M4 from its starting position.

Further, a range meter 7 is provided, which in the illustratedembodiment is mounted on the sighting instrument so as to have itsmeasuring direction parallel to the line of sight. This range meter maybe of any conventional type, such as a radar range meter, a laser rangemeter or some kind of optical range meter. It is only important that itproduces information about the range to the target being tracked eitherin the form of an electric, digital or analog signal or in the form of arotation angle of a mechanical shaft.

As shown in FIG. 2, the servomotor M3 for the azimuth movement of thesight 6 relative to the barrel 1 is supplied with a control signal froman amplifier F3 through a comparator C3. The output signal from thepotentiometer P1 coupled to the servomotor M3 is fed back in oppositionto the comparator C3. Thus the servomotor M3 is position-coupled andwill consequently rotate its shaft by an angle directly proportional tothe control signal supplied from the amplifier F3 and inverselyproportional to the signal feeding the potentiometer Pl; the lattersignal being derived from an amplifier F5 as will be described infurther detail in the following. In a similar manner the servomotor M4for the elevation movement of the sight 6 relative to the barrel 1 isconnected to a servoarnplifier F4 through a comparator C4. The outputsignal from the potentiometer P2 is fed back in opposition to thecomparator C4, whereby the shaft of the servomotor M4 is rotated by anangle directly proportional to the magnitude of the signal from theamplifier F4 and inversely proportional to the signal feeding thepotentiometer P2, said latter signal being also derived from theamplifier F5.

As explained in the foregoing, the two servomotors M3 and M4 are usedfor deflecting the line of sight of the sighting instrument 6 in azimuthand elevation respectively relative to the direction of the barrel 1 andthus the direction of fire by angles corresponding to the computed,totally required deflection angles in azimuth and elevationrespectively.

For computing the lead angles in azimuth and elevation respectivelyrequired due to the movement of the target two integrators l1 and I2 areprovided. These integrators may, through switching means K1, be suppliedwith the output signals form the tachogenerators T1 and T2 respectivelywhich are coupled respectively to the azimuth motor M1 and the elevationmotor M2 for the barrel 1.

As mentioned in the foregoing, the signal from the tachogenerator T1 isproportional to the azimuth angular velocity of the barrel 1 and thusalso to the azimuth angular velocity w, of the line of sight, whereasthe signal from the tachogenerator T2 is proportional to the elevationangular velocity w,, of the barrel 1 and thus of the line of sight,provided that the two servomotors M3 and M4 for the sight 6 arestationary in their starting positions so that the line of sight isparallel to and stationary relative the direction of the barrel 1. Theintegrated signals on the output terminals of the integrators I1 and I2can, through additional switching means K2, be connected to theamplifier F3 and the amplifier F4 respectively. Further switching meansK3 are provided for temporary short-circuiting each of the integratorsI1 and I2, whereby the integrated signals on the output terminals of theintegrators are eliminated and a new integration can be started.

The switching means K1, K2 and K3 may be mechanical contacts on a relayor solid state switches and are actuated from a timing device T, whichmay be of any conventional type, such as an electric timing circuit oran electromechanical timer. The time span of the timing device T can beadjusted or set from the range meter 7 in agreement with the measuredrange D to the target so that the time span becomes equal to a constanttimes the range D to the target. In their inactivated state all switchesK1, K2 and K3 are in the positions shown in the drawing. The timingdevice T can be started by temporary closure of a switch 8 which ismanually operated by the gunner. When the timing device T starts itcloses the switches Kl for the input signals to the integrators I1 andI2. When the timing device T runs out it reopens the switches K1 andcloses the switches K2 so that the integrated signals on the I outputterminals of the integrators I1 and I2 are applied to the amplifiers F3and F4. The timing device T can thereafter be caused to reopen theswitches K2 if and when the gunner temporarily closes an additionalmanually operated switch 9. When the switches K2 then open the switchesK3 are closed temporarily, whereby the integrators I1 and 12 are shortcircuited and the integrated signals on their output terminals areeliminated.

The range meter 7 supplies information about the range also to a numberof analog multipliers for generating signals proportional to D, D D etc.dependent on the demand for accuracy in the computation. In theillustrated embodiment of the invention there are only two suchmultipliers which consist of potentiometers P3 and P4. The potentiometerP3 is supplied with a reference voltage, which for the sake ofsimplicity is assumed to have the value 1, whereas the potentiometer P4is supplied with the output voltage from the potentiometer P3. Theoutput voltage from the potentiometer P3 is consequently proportional tothe range D to the target, whereas the output voltage from thepotentiometer P4 is proportional to D2. The output voltages from thesetwo potentiometers P3 and P4 are supplied to separate inputs of theamplifier F5, which on an additional input is also supplied with avoltage proportional to the muzzle velocity v for a fired projectile.The input voltages are summed and amplified in the amplifier F5 with thepolarities and constants given in the expression (3) so that the outputsignal from the amplifier F5 is proportional to the mean velocity v,,,for the projectile. As the signal from the amplifier F5 is supplied tothe two potentiometers P1 and P2, which generate the feed-back signalsfor the servomotors M3 and M4, the rotation angles of these servomotors,when control signals from the amplifiers F3 and F4 are applied to theservomotors, will be inversely proportional to the mean velocity v,, ofthe projectile.

The output signals from the potentiometers P3 and P4 are also suppliedto separate inputs on an amplifier F6, in which the two input signalsare summed and amplified with the constants K and k given in theexpression (5) so that the output signal from the amplifier F6 becomesproportional to 4),, v,,,, that is the product of the requiredsuperelevation (1),, and the mean velocity v,,, of the projectile. Theoutput signal from the amplifier F6 can be applied to the amplifier F4through a switch K4.

In similar manner the output signals from the two potentiometers P3 andP4 are supplied to separate inputs of an additional amplifier F7, whichsums and amplifies the two input signals in such a way that the outputsignal from the amplifier becomes proportional to the product of themean velocity v of the projectile and the deflection angle componentsnecessary for compensation of, for instance, wind forces and therotation of the projectile. The output signal from the amplifier F7 canbe supplied to the amplifier F3 through a switch K5.

In the illustrated embodiment of the invention the two switches K4 andK5 are actuated by the timing device T so as to close and opensimultaneously with the switches K2.

The device described above operates in the following manner. In thestarting state for a target tracking operation all switches Kl to K2 arein the open positions shown in FIG. 2, wherefore no control signals aresupplied to the servomotors M3 and M4 and the line of sight for thesighting instrument 6 consequently is parallel to and stationaryrelative the direction of the barrel 1. By means of the control lever 5the gunner aims the barrel 1 and thus also the line of sight directly atthe target and follows subsequently the target with the line of sight.The angular movement of the barrel and the line of sight willconsequently be equal to the angular movement of the target. In thediagram in FIG. 3 the angular positions of the target, the line of sightand the barrel are shown as functions of the time during a targettracking operation. The angular position of the target is represented bythe solid curve, whereas the angular position of the line of sight isrepresented by the dotted curve and the angular position of the barrel,that is of the direction of fire, is represented by the dash-dot curve.Further it is assumed that during all the time the target is moving witha constant angular velocity, wherefore the angular position of thetarget is a linear function of the time. During the above describedinitial stage of the target tracking operation the direction to thetarget, the line of sight and the direction of fire are obviously movingtogether uniformly. At an instant when the gunner has the line of sightaimed as accurately as possible at the target and judges that the targetwill during the immediate future probably move with unchanged velocityand direction, the gunner initiates the process for computing therequired lead angle in that he closes the switch 8 temporarily (FIG. 2).In the diagram in FIG. 3 this instant is indicated by 1-,.

When the switch 8 closes, the timing device T starts its operation andcloses simultaneously the two switches K1. Thus the two integrators I1and I2 start to integrate the signal proportional to the azimuth angularvelocity w, of the line of sight and the signal proportional to theelevation angular velocity w,, of the line of sight respectively. Thestarting of the lead angle computation does not affect the twoservomotors M3 and M4 for the sighting instrument, wherefore theseservomotors remain stationary. Neither are the servomotors M1 and M2 forthe gun affected by the starting of the lead angle computation.Consequently the gunner meets no difficulties whatsoever in maintainingthe line of sight aimed directly at the target.

When the time span 1' of the timing device T is finished, there existsconsequently an integrated signal on the output terminal of theintegrator II which is proportional to the product of the azimuthangular velocity w, of the line of sight and the range D to the target,and on the output terminal of the integrator I2 an integrated signalproportional to the product of the elevation angular velocity w of theline of sight and the range D to the target because the time span 1- ofthe timing device T is equal to a constant times the range D to thetarget as determined by the range meter 7. In the diagram in FIG. 3 theend of the computation period is indicated by 7 As described in theforegoing there exists on the output terminal of the amplifier F6permanently a signal proportional to the product of the desiredsuperelevation d) and the mean velocity v,,, of the projectile, whereason the output terminal of the amplifier F7 a signal is present which isproportional to the product of the mean velocity v, of the projecnle andthe correction angles necessary due to, for instance, wind forces,projectile rotation, etc.

At the instant 1- when the timing device T runs out, the switches K2, K4and K5 and simultaneously the switches K1 are opened, whereby theintegration in the integrators I1 and I2 is interrupted. The integratedsignals on the output terminals of the integrators and the signals onthe output terminals of the amplifiers F6 and F7 are consequentlyapplied to the servoamplifiers F3 and F4 for respectively the azimuthmotor M3 and the elevation motor M4 of the sighting instrument. Thus themotors M3 and M4 will rotate the sight 6 and deflect the line of sightrelative to the direction of the barrel 1, that is relative to thedirection of fire, in azimuth and elevation respectively by angles whichare directly proportional to the magnitudes of the control signalssupplied to the amplifiers F3 and F4 respectively and inverselyproportional to the signal supplied from the amplifier F5 to thepotentiometers P1 and P2 respectively. The latter signal is, asmentioned in the foregoing, proportional to the computed mean velocity vof the projectile. As is obvious from the expressions (4) and (5) andthe discussion connected therewith, the two servomotors M3 and M4 willdeflect the line of sight from the direction of the barrel, that is fromthe direction of fire, in azimuth and elevation respectively by a totalangle corresponding to the total desired deflection angle for the firingof a projectile against the target, that is both the lead angle requireddue to the movement of the target as well as the required superelevationand the required correction angles for wind forces, projectile rotation,etc. In the diagram in FIG. 3 this total deflection angle is designatedby 4),. As can be seen in FIG. 3, the line of sight is deflected fromthe direction of fire in such a direction that the line of sight willlag the direction of fire as seen in the direction of the targettracking. The deflection of the line of sight will be carried outsubstantially momentarily, as the two servomotors M3 and M4 have only torotate the sighting instrument 6 which has a very small weight.

As can be seen in FIG. 3, the introduction of the total computeddeflection angle qb, between the line of sight and the direction of firecauses that the line of sight is moved away from the target.Consequently the gunner must as soon as possible return the line ofsight onto the target by means of the control lever 5 the barrel 1 andthus also the line of sight. During this process the barrel, that is thedirection of fire, and the line of sight move of course uniformly sothat the mutual total deflection angle dz, between them is maintained.As soon as the gunner has returned the line of sight onto the target aprojectile can be fired. Of course also several projectiles can be firedusing the same deflection angle between the direction of fire and theline of sight. If, however, the gunner should wish to perform a newcomputation of the necessary lead angle before a new projectile isfired, he can do this by closing the switch 9 temporarily. This causesthe switches K2, K4 and K5 to be reopened, whereby the servomotors M3and M4 return the line of sight to a position parallel to the directionof the barrel ll. At the same time the integrators I1 and I2 aretemporarily short-circuited by the switches K3 so that the integratedsignals on the output terminals of the integrators are eliminated.Thereafter the gunner can start a new computation of the lead angle byclosing the switch 8 in the manner described in the foregoing.

One disadvantage of the device according to the invention which has beendescribed above is that at the end of the computation interval the lineof sight is momentarily moved away from the target, whereby the gunnerloses the target and has to return the line of sight onto the target bymeans of the control lever 5 before a projectile can be fired. Thismakes the task of the gunner more difficult and at the same time thefiring of a projectile is delayed.

However, this disadvantage can be eliminated by a modification of thedevice according to the invention in which, as illustrated by dottedlines in FIG. 2, each of two servomotors M3 and M4 for the sight 6 iscoupled to a signal generator T3 and T4 respectively, for instance atachogenerator, generating a signal proportional to the rate of rotationof the associated servomotor. The signal form the tachogenerator T3coupled to the azimuth motor M3 of the sight is applied as an additionalcontrol signal to the azimuth servomotor Ml of the barrel 1 with such apolarity that this additional control signal assists the control signalform the signal generator S1 coupled to the lever 5. In similar mannerthe signal from the tachogenerator T4 coupled to the elevation motor M4of the sight is applied as an additional control signal to the elevationservomotor M2 of the barrel 1. Thus when the two servomotors M3 and M4for the sighting instrument are started for introducing the computeddeflection angle in azimuth and elevation respectively between the lineof sight and the direction of fire of the barrel 1, the barrel will, dueto the above described modified arrangement, be given an increasedazimuth angular velocity and elevation angular velocity respectively.The magnitude of this increase exactly corresponds to the azimuthangular velocity and the elevation angular velocity respectively thatare imparted to the line of sight by the servomotors M3 and M4 relativeto the barrel 1. In this way the line of sight will be maintainedpointed at the target without the gunner having to operate the controllever 5, whereas the barrel 1, that is the direction of fire, is movedforward in the direction of the target tracking by an anglecorresponding to the computed total deflection angle.

In the foregoing the invention has been described with reference to aweapon and sight system in which the sighting instrument is mounted onthe layable portion of the weapon so that the gunner can keep the lineof sight pointed at the target by controlling the servomotors laying theweapon. However, the invention can also be used in weapon and sightsystems in which the weapon and the sighting instrument are separate andindividually layable relative to a support, as for instance the ground.In this case, however, the gunner must, by means of a control lever,control the servomotors laying the sighting instrument relative to thesupport so that the line of sight is maintained pointed at the target,while the direction of fire of the weapon is caused to move uniformlywith the line of sight in that the servomotors laying the weapon aresupplied with control signals derived from position detectors coupled tothe servomotors of the sighting instrument. The servomotors belonging tothe lead angle computer (corresponding to the servomotors M3 and M4 inFIG. 2) are in this case not coupled to either the sighting instrumentor the weapon but rotate instead position signal generators whichgenerate signals proportional to the computed total deflection angle inazimuth and elevation respectively. At the end of the computationinterval these signals are applied to the servomotors laying the weaponas additional control signals, whereby the direction of fire of theweapon is deflected from the line of sight in the direction of thetarget tracking by the computed total deflection angle.

In the embodiment of the invention described by way of example it hasalso been assumed that the direction of fire of the weapon and the lineof sight are parallel during the target tracking and the integrationinterval. Fundamentally this is not necessary. Thus for instance at thebeginning of the computation interval there may exist a deflection anglebetween the direction of fire of the weapon and the line of sightcorresponding to those deflection angle components that are independentof the movement of the target, such as the superelevation andcompensations for wind forces and the projectile rotation. It isessential, however, that during the computation interval the directionof fire of the weapon and the line of sight move uniformly without anymutual angular velocity relative each other so that the target trackingprocess is not affected by any disturbances during the computationinterval.

Further, in the embodiment of the invention described in the foregoingthe azimuth angular velocity and the elevation angular velocity of theline of sight are measured by means of tachogenerators coupled to theazimuth motor and the elevation motor of the weapon respectively.However, the angular velocities of the line of sight can of course alsobe measured in other ways, for instance by rate gyros mounted on aportion of the weapon which is directed in azimuth and elevationrespectively. Such an arrangement will for instance be necessary if theweapon is stationary in a vehicle and is laid by movements of the entirevehicle.

What is claimed is:

1. In a weapon and sight system including an angularly rotatable weaponand sighting instrument with an angularly rotatable line of sight themethod of providing a correct lead angle between the direction of fireof the weapon and the line of sight of the sighting instrument whenfiring a projectile from the weapon against a moving target comprisingthe steps of:

moving the line of sight of the sighting instrument so as to keep itpointing at the moving target;

rotating said weapon so as to move the direction of fire thereofuniformly with the movement of the line of sight of the sightinginstrument without any relative angular velocity between the directionof fire and the line of sight;

continuously measuring the angular velocity of the line of sight;

integrating the angular velocity of the line of sight over apredetermined limited time interval;

at the end of said time interval substantially momentarily deflectingthe direction of fire of said weapon and the line of sight of saidsighting instrument from each other by an angle proportional to theintegrated value of the angular velocity of the line of sight in suchrelative direction that the direction of fire of the weapon will leadthe line of sight of the sighting instrument as seen in the direction ofthe angular movement of the target; and

subsequently continuing to move the direction of fire of said weaponuniformly with the movement of the line of sight of the sightinginstrument until a projectile is fired against the target.

2. The method as claimed in claim 1, wherein said limited time intervalis selected to be equal to the product of a constant and the range tothe moving target, and at the end of the limited time interval the lineof sight of the sighting instrument and the direction of fire of theweapon are deflected from each other by an angle proportional to theintegrated value of the angular velocity of the line of sight divided bythe mean velocity of a projectile fired at the target.

3. The method as claimed in claim 1, comprising the additional step atthe end of said limited time interval of momentarily deflecting the lineof sight of said sighting instrument and the direction of fire of saidweapon from each other not only by said angle proportional to theintegrated value of the angular velocity of the line of sight but alsoby a computed superelevation angle and computed correction angles forwind forces acting upon a projectile fired at the target and for therotation of the projectile.

4. A weapon and sight system comprising:

an angularly rotatable weapon;

a sighting instrument with an angularly rotatable line of sight, saidweapon and said sighting instrument being coupled to each other so thatthe line of sight of the sighting instrument and the direction of fireof the weapon normally move uniformly without any relative angularvelocity;

first servo-drive means for angularly rotating the line of sight of saidsighting instrument;

manually operable means for generating a manually variable controlsignal for said first servodrive means for tracking a moving target withthe line of sight of the sighting instrument; and

lead angle computing means for providing a correct lead angle betweenthe direction of fire of the weapon and the line of sight of thesighting instrument when firing a projectile at the target beingtracked,

said lead angle computing means comprising means for measuring theangular velocity of the line of sight of the sighting instrument andproducing a signal proportional thereto,

timing means for determining a time interval proportional to the rangeto the target being tracked,

means for initiating the operation of said timing means at a selectedinstant,

signal integrating means,

second servodrive means for angularly deflecting the direction of fireof said weapon and the line of sight of said sighting instrument fromeach other by an angle proportional to a control signal supplied to saidsecond servo-drive means,

first switching means responsive to the operation of said timing meansto apply said signal proportional to the angular velocity of the line ofsight of the sighting instrument to the input of said signal integratingmeans during said time interval,

and second switching means responsive to the operation of said timingmeans to apply at the end of said time interval the output signal ofsaid signal integrating means as a control signal to said secondservo-drive means.

5. The weapon and sight system as claimed in claim 4, wherein saidtiming means is adapted to determine a time interval equal to theproduct of a constant and the range to the target being tracked, saidsecond servodrive means including rotating servomotor means and signalgenerating means coupled to said servomotor means for generating anegative feed-back signal for said servomotor means proportional to theproduct of the angle of rotation of said servomotor means and areference signal supplied to said signal generating means, and whereinsaid lead angle computing means comprise means for computing the meanvelocity for a projectile fired at the target being tracked andproducing a signal proportional to said mean velocity, said signal beingsupplied to said signal generating means as said reference signal.

6. A weapon and sight system as claimed in claim 5, wherein said firstservo-drive means is adapted to angularly rotate said weapon, saidsighting instrument is mounted on said weapon so as to participate inits movements, and said servomotor means of said second servo-drivemeans is adapted to angularly rotate the line of sight of the sightinginstrument relative to the direction of fire of the weapon.

7. A weapon and sight system as claimed in claim 6, comprising secondsignal generating means coupled to said servomotor means of said secondservo-drive means for generating a signal representing the rotation ofsaid servomotor means, said signal being applied to said firstservo-drive means for rotating said weapon as an additional controlsignal assisting said manually variable control signal.

1. In a weapon and sight system including an angularly rotatable weaponand sighting instrument with an angularly rotatable line of sight themethod of providing a correct lead angle between the direction of fireof the weapon and the line of sight of the sighting instrument whenfiring a projectile from the weapon against a moving target comprisingthe steps of: moving the line of sight of the sighting instrument so asto keep it pointing at the moving target; rotating said weapon so as tomove the direction of fire thereof uniformly with the movement of theline of sight of the sighting instrument without any relative angularvelocity between the direction of fire and the line of sight;continuously measuring the angular velocity of the line of sight;integrating the angular velocity of the line of sight over apredetermined limited time interval; at the end of said time intervalsubstantially momentarily deflecting the direction of fire of saidweapon and the line of sight of said sighting instrument from each otherby an angle proportional to the integrated value of the angular velocityof the line of sight in such relative direction that the direction offire of the weapon will lead the line of sight of the sightinginstrument as seen in the direction of the angular movement of thetarget; and subsequently continuing to move the direction of fire ofsaid weapon uniformly with the movement of the line of sight of thesighting instrument until a projectile is fired against the target. 2.The method as claimed in claim 1, wherein said limited time interval isselected to be equal to the product of a constant and the range to themoving target, and at the end of the limited time interval the line ofsight of the sighting instrument and the direction of fire of the weaponare deflected from each other by an angle proportional to the integratedvalue of the angular velocity of the line of sight divided by the meanvelocity of a projectile fired at the target.
 3. The method as claimedin claim 1, compRising the additional step at the end of said limitedtime interval of momentarily deflecting the line of sight of saidsighting instrument and the direction of fire of said weapon from eachother not only by said angle proportional to the integrated value of theangular velocity of the line of sight but also by a computedsuperelevation angle and computed correction angles for wind forcesacting upon a projectile fired at the target and for the rotation of theprojectile.
 4. A weapon and sight system comprising: an angularlyrotatable weapon; a sighting instrument with an angularly rotatable lineof sight, said weapon and said sighting instrument being coupled to eachother so that the line of sight of the sighting instrument and thedirection of fire of the weapon normally move uniformly without anyrelative angular velocity; first servo-drive means for angularlyrotating the line of sight of said sighting instrument; manuallyoperable means for generating a manually variable control signal forsaid first servodrive means for tracking a moving target with the lineof sight of the sighting instrument; and lead angle computing means forproviding a correct lead angle between the direction of fire of theweapon and the line of sight of the sighting instrument when firing aprojectile at the target being tracked, said lead angle computing meanscomprising means for measuring the angular velocity of the line of sightof the sighting instrument and producing a signal proportional thereto,timing means for determining a time interval proportional to the rangeto the target being tracked, means for initiating the operation of saidtiming means at a selected instant, signal integrating means, secondservodrive means for angularly deflecting the direction of fire of saidweapon and the line of sight of said sighting instrument from each otherby an angle proportional to a control signal supplied to said secondservo-drive means, first switching means responsive to the operation ofsaid timing means to apply said signal proportional to the angularvelocity of the line of sight of the sighting instrument to the input ofsaid signal integrating means during said time interval, and secondswitching means responsive to the operation of said timing means toapply at the end of said time interval the output signal of said signalintegrating means as a control signal to said second servo-drive means.5. The weapon and sight system as claimed in claim 4, wherein saidtiming means is adapted to determine a time interval equal to theproduct of a constant and the range to the target being tracked, saidsecond servo-drive means including rotating servomotor means and signalgenerating means coupled to said servomotor means for generating anegative feed-back signal for said servomotor means proportional to theproduct of the angle of rotation of said servomotor means and areference signal supplied to said signal generating means, and whereinsaid lead angle computing means comprise means for computing the meanvelocity for a projectile fired at the target being tracked andproducing a signal proportional to said mean velocity, said signal beingsupplied to said signal generating means as said reference signal.
 6. Aweapon and sight system as claimed in claim 5, wherein said firstservo-drive means is adapted to angularly rotate said weapon, saidsighting instrument is mounted on said weapon so as to participate inits movements, and said servomotor means of said second servo-drivemeans is adapted to angularly rotate the line of sight of the sightinginstrument relative to the direction of fire of the weapon.
 7. A weaponand sight system as claimed in claim 6, comprising second signalgenerating means coupled to said servomotor means of said secondservo-drive means for generating a signal representing the rotation ofsaid servomotor means, said signal being applied to said firstservo-drive means for rotating said weapon As an additional controlsignal assisting said manually variable control signal.